U.S. patent application number 11/328398 was filed with the patent office on 2006-07-13 for method of medium access control for a wireless system and a relay station used in a wireless system.
This patent application is currently assigned to KDDI Corporation. Invention is credited to Kenji Saito.
Application Number | 20060153132 11/328398 |
Document ID | / |
Family ID | 36653144 |
Filed Date | 2006-07-13 |
United States Patent
Application |
20060153132 |
Kind Code |
A1 |
Saito; Kenji |
July 13, 2006 |
Method of medium access control for a wireless system and a relay
station used in a wireless system
Abstract
The present invention relates to an method of medium access
control for a wireless system that makes possible a subscriber
station located out of coverage area of a base station communicate
with the base station with the help of a relay station. The method
includes broadcasting a polling packet by the relay station during
the contention period, receiving the polling packet by the relayed
subscriber station, transmitting a packet by the relayed subscriber
station to the relay station during a predetermined period, and
transmitting the packet to the base station by the relay station in
the contention period after passing the predetermined period.
Inventors: |
Saito; Kenji; (Saitama,
JP) |
Correspondence
Address: |
MARTIN NOVACK
16355 VINTAGE OAKS LANE
DELRAY BEACH
FL
33484
US
|
Assignee: |
KDDI Corporation
|
Family ID: |
36653144 |
Appl. No.: |
11/328398 |
Filed: |
January 9, 2006 |
Current U.S.
Class: |
370/329 ;
370/346 |
Current CPC
Class: |
H04W 74/06 20130101;
H04B 7/155 20130101; H04B 7/2606 20130101 |
Class at
Publication: |
370/329 ;
370/346 |
International
Class: |
H04Q 7/00 20060101
H04Q007/00; H04J 3/16 20060101 H04J003/16 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 11, 2005 |
JP |
3917/2005 |
Claims
1. A method of medium access control for a wireless system
comprising a base station, a relay station being able to
communicate with the base station, a first subscriber station being
able to communicate with the base station, and a second subscriber
station being unable to communicate with the base station and being
able to communicate with the relay station, the method comprising
the steps of: broadcasting a polling packet by the relay station
during the contention period; receiving the polling packet by the
second subscriber station; transmitting a packet by the second
subscriber station to the relay station during a predetermined
period; and transmitting the packet to the base station by the
relay station in the contention period after passing the
predetermined period, wherein the first subscriber station stop
transmitting any packets during the predetermined period, in case
it receives the polling packet.
2. The method of claim 1, wherein the system is in accordance with
the distributed coordinated function (DCF) of IEEE 802.11 standard
and the contention period is provided after DCF interframe space
(DIFS).
3. The method of claim 1, wherein the system is in accordance with
point to multipoint mode of the IEEE 802.16 standard, wherein the
packet transmitted from the second subscriber station to the base
station via the relay station is for a ranging request (RNG-REQ)
message or for a bandwidth request (BW-REQ) message.
4. The method of claim 1, further comprising the step of:
broadcasting a downlink frame by the relay station to the second
subscriber station, in case the relay station receives the downlink
frame from the base station; and transmitting the RNG-REQ message
or the BW-REQ message by the relay station after passing the
predetermined period, in case the relay station receives the
RNG-REQ message or the BW-REQ message from the second subscriber
station.
5. The method of claim 4, wherein the relay station sets the value
of start time field of both DL-MAP and UL-MAP included in the
broadcasting downlink frame, the value is subtracted transmission
delay between the base station and the relay station from a value
in the start time field of DL-MAP and UL-MAP included in the
receiving downlink frame from the base station.
6. A relay station for a wireless system comprising a base station,
a first subscriber station being able to communicate with the base
station, and a second subscriber station being unable to
communicate with the base station and being able to communicate
with the relay station, the relay station being able to communicate
with the base station, the relay station comprising: means for
transmitting a polling packet during the contention period, the
polling packet making the first subscriber station stop
transmitting any packets; means for receiving a packet from the
second subscriber station in the contention period; and means for
transmitting the packet received from the second subscriber station
to the base station after passing a predetermined period.
7. The relay station of claim 6, wherein the system is in
accordance with the distributed coordinated function (DCF) of IEEE
802.11 standard and the contention period is provided after DCF
interframe space (DIFS).
8. The relay station of claim 6, wherein the system is in
accordance with point to multipoint mode of the IEEE 802.16
standard, wherein the packet transmitted from the second subscriber
station to the base station via the relay station is for a ranging
request (RNG-REQ) message or for a bandwidth request (BW-REQ)
message.
9. The relay station of claim 8, further comprising: means for
broadcasting a downlink frame to the second subscriber station, in
case the relay station receives the downlink frame from the base
station; and means for transmitting the RNG-REQ message or the
BW-REQ message to the base station after passing the predetermined
period, in case the relay station receives the RNG-REQ message or
the BW-REQ message from the second subscriber station.
10. The relay station of claim 9, further comprising: means for
setting a value of start time field of both DL-MAP and UL-MAP
included in the broadcasting downlink frame, the value is
subtracted transmission delay between the base station and the
relay station from a value in the start time field of DL-MAP and
UL-MAP included in the receiving downlink frame from the base
station.
11. A computer program product for a relay station for a wireless
system comprising a base station, the relay station being able to
communicate with the base station, a first subscriber station being
able to communicate with the base station, and a second subscriber
station being unable to communicate with the base station and being
able to communicate with the relay station, the computer program
product comprising: first instruction means for transmitting a
polling packet during the contention period, the polling packet
making the first subscriber station stop transmitting any packets;
second instruction means for receiving a packet from the second
subscriber station in the contention period; and third instruction
means for transmitting the packet received from the second
subscriber station to the base station after passing a
predetermined period.
12. The computer program product of claim 11, wherein the system is
in accordance with the distributed coordinated function (DCF) of
IEEE 802.11 standard and the contention period is provided after
DCF interframe space (DIFS).
13. The computer program product of claim 11, wherein the system is
in accordance with point to multipoint mode of the IEEE 802.16
standard, wherein the packet transmitted from the second subscriber
station to the base station via the relay station is for a ranging
request (RNG-REQ) message or for a bandwidth request (BW-REQ)
message.
14. The computer program product of claim 13, further comprising:
fourth instruction means for broadcasting a downlink frame to the
second subscriber station, in case the relay station receives the
downlink frame from the base station; and fifth instruction means
for transmitting the RNG-REQ message or the BW-REQ message to the
base station after passing the predetermined period, in case the
relay station receives the RNG-REQ message or the BW-REQ message
from the second subscriber station.
15. The computer program product of claim 9, further comprising:
sixth instruction means for setting a value of start time field of
both DL-MAP and UL-MAP included in the broadcasting downlink frame,
the value is subtracted transmission delay between the base station
and the relay station from a value in the start time field of
DL-MAP and UL-MAP included in the receiving downlink frame from the
base station.
Description
PRIORITY CLAIM
[0001] This application claims priority from Japanese patent
application No. 2005-003917, filed on Jan. 11, 2005, which is
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a method of medium access
control for a wireless system and a relay station used in the
wireless system.
[0004] 2. Description of the Related Art
[0005] For wireless local area network (LAN), it has been widely
used a system in accordance with IEEE 802.11 standard. Also
practical application of high data rate wireless access system,
such as IEEE 802.16, is studied. IEEE 802.16 is a standard for
broadband wireless access (BWA) used in wireless metropolitan area
network (MAN), realizes wider coverage area and higher data rate
compared to IEEE 802.11, and performs quality of service (QoS)
control precisely. Especially, it achieves data rate more than 120
Mbps at 2 GHz to 66 GHz frequency band, if line-of-sight is
available.
[0006] There is a wireless system that a base station (BS) controls
medium access with one or more subscriber stations (SS) placed in
its coverage area. This system is defined as infrastructure mode in
IEEE 802.11 and as point-to-multipoint (PMP) mode in IEEE 802.16.
In these modes, communication method between a base station and
subscriber stations via relay station (RS) is not specified.
[0007] On the contrary, there is another wireless system that has
no base station BS, and subscriber stations establish peer-to-peer
or multi hop network autonomously. This system is defined as ad hoc
mode in IEEE 802.11, and defined as mesh mode in IEEE 802.16. In
accordance with these modes, one subscriber station communicates
with another subscriber station via one or more subscriber
stations, that is multi hop configuration.
[0008] In IEEE 802.11, wireless distribution system (WDS) is also
defined. With WDS, packets can be relayed between base stations
configured as infrastructure mode. This system is under
consideration by the task group S of IEEE 802.11.
[0009] Further, even if a first subscriber station and a second
subscriber station can communicate with an access point of wireless
LAN system, collision between packets, which is sent by these
subscribers, may occur, in case the first subscriber station and
the second subscriber station can not communicate each other. This
problem is referred as "hidden terminal problem". For "hidden
terminal problem", IEEE 802.11 specifies a request to send (RTS)
message and a clear to send (CTS) message. JP patent publication
2001-231078 disclose the method for controlling packet transmission
between relay stations using RTS/CTS packets, to avoid bad effect
on one relay station caused by the packet from other relay
stations. This method makes processing time for relaying short, and
avoids packets from staying in one relay station for a long
time.
[0010] More precisely, for receiving confirmation of data packets
from a first relay station, a second relay station sends a RTS
packet to the first relay station, instead of an ACK packet. The
first relay station recognizes the second relay station receives
data packets by receiving the RTS packet from the second relay
station, and stop packets transmission for the period described in
the RTS packet. The RTS packet sent from the second relay station
is also received by a third relay station. The third relay station
sends a CTS packet to the second relay station after SIFS (Short
InterFrame Space) period, if the third relay station is ready to
receive data packets. The second relay station recognizes the third
relay station is ready by receiving the CTS packet from the third
relay station, and sends data packets to the third relay station
after SIFS period.
[0011] Regarding as the above mentioned art, it is impossible to
use ad hoc mode and infrastructure mode simultaneously in
accordance with IEEE 802.11, because it requires to set
identification flag that indicates the operation mode in the frame.
Also it is impossible to use mesh mode and PMP mode simultaneously
in accordance with IEEE 802.16, because a frame structure used in
the mesh mode and one used in the PMP mode is completely different,
and is not compatible. Therefore, subscriber station, which is out
of coverage area of a base station, cannot communicate with the
base station, even if there is a relay station, with which the
subscriber station can communicate, in the coverage area of the
base station. Especially, in case of the system based on the IEEE
802.16 standard, it is distant, because operating mode of the whole
system must be changed.
[0012] Furthermore, data throughput of mesh mode decreases compared
to the one of PMP mode, because mesh mode need to send more
management information than PMP mode. Also mesh mode is defined as
optional, a subscriber station, which is implemented only PMP mode,
cannot communicate with base station via relay station.
[0013] Because the system in accordance with IEEE 802.16 is used
with the frequency band above 2 GHz, which is very sensitive to the
land feature and buildings, communication is easy to unstable.
Therefore, if the subscriber station is in the building or
basement, it could not probably communicate with the base station.
In this case, new base station should be provided.
BRIEF SUMMARY OF THE INVENTION
[0014] The invention has been made in view of the above-mentioned
problem, and it is therefore an object of the present invention to
provide a method for medium access control of a wireless system
that makes possible a subscriber station located out of coverage
area of a base station can communicate with the base station via a
relay station, which is in the coverage area of the base station.
The present invention also provides the relay station used in the
wireless system.
[0015] According to the present invention, a method of medium
access control for a wireless system, which has a base station, a
relay station that can communicate with the base station, a first
subscriber station that can communicate with the base station, and
a second subscriber station that can communicate with the relay
station, but can not communicate with the base station, the method
includes the steps of broadcasting a polling packet by the relay
station during the contention period, receiving the polling packet
by the second subscriber station, transmitting a packet by the
second subscriber station to the relay station during a
predetermined period, and transmitting the packet to the base
station by the relay station in the contention period after passing
the predetermined period. The first subscriber station stops
transmitting any packets during the predetermined period, in case
it receives the polling packet.
[0016] Favorably, the method is applied to the system in accordance
with the distributed coordinated function (DCF) of IEEE 802.11
standard, and the contention period is provided after DCF
interframe space (DIFS).
[0017] Favorably, the method is applied to the system in accordance
with point to multipoint mode of the IEEE 802.16 standard, and the
packet transmitted from the second subscriber station to the base
station via the relay station is for a ranging request (RNG-REQ)
message or for a bandwidth request (BW-REQ) message.
[0018] Advantageously, the method further includes the step of
broadcasting a downlink frame by the relay station to the second
subscriber station, in case the relay station receives the downlink
frame from the base station, and transmitting the RNG-REQ message
or the BW-REQ message after passing the predetermined period, in
case the relay station receives the RNG-REQ message or the BW-REQ
message from the second subscriber station.
[0019] Favorably, the relay station sets the value of start time
field of both DL-MAP and UL-MAP included in the broadcasting
downlink frame, the value is subtracted transmission delay between
the base station and the relay station from a value in the start
time field of DL-MAP and UL-MAP included in the receiving downlink
frame from the base station.
[0020] According to another aspect of the present invention, a
relay station is used for a wireless system, which has a base
station, a first subscriber station that can communicate with the
base station, and a second subscriber station that can communicate
with the relay station, but can not communicate with the base
station. The relay station can communicate with the base station,
and includes means for transmitting a polling packet, which makes
the first subscriber station stop transmitting any packets, during
the contention period, means for receiving a packet from the second
subscriber station in the contention period, and means for
transmitting the packet received from the second subscriber station
to the base station after passing a predetermined period.
[0021] Favorably, the relay station is applied to the system in
accordance with the distributed coordinated function (DCF) of IEEE
802.11 standard and the contention period is provided after DCF
interframe space (DIFS).
[0022] Favorably, the relay station is applied to the system in
accordance with point to multipoint mode of the IEEE 802.16
standard, and the packet transmitted from the second subscriber
station to the base station via the relay station is for a ranging
request (RNG-REQ) message or for a bandwidth request (BW-REQ)
message.
[0023] Advantageously, the relay station further includes means for
broadcasting a downlink frame to the second subscriber station, in
case the relay station receives the downlink frame from the base
station, and means for transmitting the RNG-REQ message or the
BW-REQ message to the base station after passing the predetermined
period, in case the relay station receives the RNG-REQ message or
the BW-REQ message from the second subscriber station.
[0024] Advantageously, the relay station further includes means for
setting a value of start time field of both DL-MAP and UL-MAP
included in the broadcasting downlink frame, where the value is
subtracted transmission delay between the base station and the
relay station from a value in the start time field of DL-MAP and
UL-MAP included in the receiving downlink frame from the base
station.
[0025] According to further aspect of the present invention, the
relay station is implemented by computer program, which is stored
on a computer readable medium.
[0026] According to the present invention, the base station can
communicate with the subscriber station located out of coverage
area of the base station via the relay station. That is, the
present invention makes wider the coverage area of the base station
with the simple relay station.
[0027] Especially, point to multipoint mode of IEEE 802.16 requires
fewer overheads than the mesh mode of it, therefore it does not
reduce the throughput. Also the subscriber station that is
implemented only point to multipoint mode can communicate with the
base station with the help of the relay station.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1 is a sequence diagram of the present invention being
applied to a wireless LAN system in accordance with IEEE
802.11;
[0029] FIG. 2 is a first sequence diagram of the present invention
being applied to the wireless broadband access system in accordance
with IEEE 802.16;
[0030] FIG. 3 is a second sequence diagram of the present invention
being applied to the wireless broadband access system in accordance
with IEEE 802.16;
[0031] FIG. 4 is a third sequence diagram of the present invention
being applied to the wireless broadband access system in accordance
with IEEE 802.16;
[0032] FIG. 5 shows a structure of DL-MAP sent by the relay
station;
[0033] FIG. 6 shows a structure of UL-MAP sent by the relay
station;
[0034] FIG. 7 is a fourth sequence diagram of the present invention
being applied to the wireless broadband access system in accordance
with IEEE 802.16;
[0035] FIG. 8 shows a frame structure of a polling packet according
the present invention;
[0036] FIG. 9 shows a frame structure of a RNG-REQ message sent by
the subscriber station to the relay station;
[0037] FIG. 10 shows a frame structure of a RNG-REQ message sent by
the relay station to the base station;
[0038] FIG. 11 is a fifth sequence diagram of the present invention
being applied to the wireless broadband access system in accordance
with IEEE 802.16;
[0039] FIG. 12 is a sixth sequence diagram of the present invention
being applied to the wireless broadband access system in accordance
with IEEE 802.16; and
[0040] FIG. 13 shows a frame structure in accordance with IEEE
802.16.
DETAILED DESCRIPTION OF THE INVENTION
[0041] An embodiment of the present invention will be described
below with reference to the drawings.
[0042] FIG. 1 is a sequence diagram of the present invention being
applied to a wireless LAN system in accordance with IEEE
802.11.
[0043] The wireless system shown in FIG. 1 has a base station BS, a
relay station RS that can communicate with the base station BS and
one or more subscriber stations SS that cannot communicate with the
base station BS, but can communicate with the relay station RS.
[0044] The relay station RS waits until DIFS period, which is the
predetermined period in the contention period, is over according to
the DCF (Step S101). After DIFS period, the relay station RS
further waits until back-off period is over. The back-off period is
calculated based on contention windows (CW) generated randomly at
each station (Step S102). Then the relay station RS senses the
carrier in the system to detect packet transmission from other
stations. In case there is no data packet transmission, the relay
station RS broadcasts a polling packet. The polling packet has
predetermined format that is recognized by all stations, and CTS
packet with broadcast address for destination address field can be
used for it. Subscriber stations SS1 and SS2 receive the polling
packet transmitted by the relay station RS.
[0045] According to the present invention, the polling packet sent
by the relay station RS is also received by the base station BS as
well as other subscriber stations, which can communicate with the
base station BS. The base station BS and other subscriber stations
that do not require the relay station RS stop sending any packets
for predetermined period. On the contrary, the subscriber stations,
which send data packets to the base station BS via the relay
station RS, shift to contention period state by receiving the
polling packet, and can send data packets.
[0046] The subscriber station SS1 that receives the polling packet
waits until the back-off period, which is also calculated based on
CWs generated randomly at the subscriber station SS1, is over. Then
the subscriber station SS1 sends data packets after confirming no
carrier from other stations (Step S103). The subscriber station SS2
that receives the polling packet also waits until the back-off time
is over, and then confirms whether data packets can be transmitted
or not, as the subscriber station SS1 does. Because the subscriber
station SS2 detect data packets sent by the subscriber station SS1,
data packet transmission is delayed. Therefore no collision occurs,
and the relay station RS receives data packets from the subscriber
station SS1 (Step S104). After DIFS period, the subscriber station
SS2 further waits until the back-off period is over, and then sends
data packets, which were delayed to avoid the collision, to the
relay station RS (Step S105). After predetermined period from
sending the polling packet, the relay station RS shift to
contention period state with the base station BS, and sends data
packets received from the subscriber stations SS1 and SS2 (Step
S106).
[0047] Next, the sequence diagram of the present invention, which
is applied to a wireless broadband access system in accordance with
IEEE 802.16, is explained.
[0048] According to the present invention, PMP mode is used as the
network topology. As shown in FIG. 2, a wireless system has a relay
station RS1 and a relay station RS2, both of which are in the
coverage area of a base station BS. Also it has subscriber stations
SS-1 and SS-2, both of which are located out of coverage area of
the base station BS, but in coverage area of the relay station
RS1.
[0049] According to the IEEE 802.16, data transmission on downlink
and uplink is performed alternately and synchronously, where
downlink is the link from a base station to subscriber stations,
and uplink is the link from a subscriber station to a base station.
A frame structure based on time division duplex (TDD) has a
downlink sub-frame and an uplink sub-frame as shown in FIG. 13,
each of them has a plurality of physical slots (PS). It is possible
to adjust the position of Tx/Rx transition gap (TTG), which is
boundary of the downlink sub-frame and the uplink sub-frame, and it
means transmission bandwidth of downlink and uplink can be
configured as asymmetrically.
[0050] The downlink sub-frame includes preamble, FCH and DL burst
#k, where k is integer. DL burst #1 includes UCD (Uplink Channel
Descriptor), which is the uplink channel information, DCD (Downlink
Channel Descriptor), which is the downlink channel information,
DL-MAP and UL-MAP. The uplink sub-frame following TTG includes
contention slots for initial ranging, contention slots for BW
request (BandWidth Request) and one or more data fields for each
subscriber station. The initial ranging and BW request are within
the contention period, and data fields are within the contention
free period.
[0051] FIG. 2 is a first sequence diagram of the present invention
being applied for the wireless broadband access system in
accordance with IEEE 802.16.
[0052] The base station BS broadcasts the downlink sub-frame
including UCD, DCD, DL-MAP and UL-MAP. This downlink sub-frame is
received by the relay stations RS1 and RS2, each of which are
located inside the coverage area of the base station BS. The relay
station RS1 and RS2 establish synchronization with the base station
BS, when they receive the downlink sub-frame from the base station
BS (Step S201). The relay station RS1 sends a RNG-REQ (Ranging
Request) message to the base station BS during the initial ranging
period after TTG, which is the boundary of the downlink sub-frame
and uplink sub-frame. The information for adjusting timing and
transmission power is included in the RNG-REQ message. Preferably,
it may use CSMA/CA (Carrier Sense Multiple Access with Collision
Avoidance), which is the method each station sends data packet
after confirming no carrier on the transmission medium for
predetermined period, for packets transmission during the
contention slots. The RNG-REQ message is sent after back-off period
corresponding to the contention windows (Step S202). The relay
station RS2 also sends a RNG-REQ message to the base station BS
during initial ranging period (Step S203).
[0053] FIG. 3 is a second sequence diagram of the present invention
being applied to the wireless broadband access system in accordance
with IEEE 802.16.
[0054] The base station BS broadcasts the downlink sub-frame
including UCD, DCD, DL-MAP and UL-MAP (Step S204). This downlink
sub-frame also includes a RNG-RSP (Ranging Response) message, which
is the reply against the RNG-REQ message sent by the relay stations
RS1 and RS2. The relay stations RS1 and RS2 complete ranging by
receiving the RNG-RSP message (Step S205). The relay station RS1
sends a BW-REQ message (Bandwidth Request) to the base station BS
during the bandwidth request period in the contention slots after
TTG, which is the boundary of the downlink sub-frame and uplink
sub-frame. Preferably, the BW-REQ message may be transmitted based
on CSMA/CA. The BW-REQ message is for requesting bandwidth for a
REG-REQ (Registration Request) message transmitted in the next
phase shown in FIG. 4. The BW-REQ message is sent after backoff
period corresponding to the contention windows (Step S206). The
relay station RS2 also sends a BW-REQ message to the base station
BS during the bandwidth request period in the contention slots
(Step S207).
[0055] FIG. 4 is a third sequence diagram of the present invention
being applied to the wireless broadband access system in accordance
with IEEE 802.16.
[0056] The base station BS broadcasts the downlink sub-frame
including UCD, DCD, DL-MAP and UL-MAP (Step S208). The relay
station RS1 broadcasts the downlink sub-frame received from the
base station BS. The subscriber stations SS1-1 and SS1-2 establish
synchronization with the relay station RS, when they receive the
downlink sub-frame from the relay station RS1. The relay station
RS2 also broadcasts the downlink sub-frame received from the base
station BS. (Step S209). The relay station RS1 sends a REG-REQ
message to the base station BS after contention slots. The REG-REQ
message is transmitted in accordance with UL-MAP, which is
generated as the reply of the BW-REQ message, and transmitted
during the contention free period (Step S210). The relay station
RS2 also sends a REG-REQ message to the base station BS (Step
S211).
[0057] FIG. 5 shows a structure of DL-MAP sent by the relay
stations RS1 and RS2. FIG. 6 shows a structure of UL-MAP sent by
the relay stations RS1 and RS2.
[0058] According to the invention, the relay stations RS1 and RS2
change the value of start time in the DL-MAP and UL-MAP. More
precisely, start time in the DL-MAP and UL-MAP sent to subscriber
stations has the value that is subtracted transmission delay time
from the start time in the DL-MAP and UL-MAP sent by the base
station BS. For example, the downlink sub-frame sent by the base
station BS at step S208 in FIG. 4 reaches to the relay station RS1
T11 time later. Therefore the relay station RS1 broadcasts downlink
sub-frame T11 time later. For the subscriber stations SS1-1 and
SS1-2, the time when the relay station RS1 broadcasts downlink
sub-frame is reference. Therefore start time in the DL-MAP and
UL-MAP to the subscriber stations SS1-1 and SS1-2 has a value that
is subtracted transmission delay T11 from the start time in the
DL-MAP and UL-MAP received from the base station BS. If no
subtraction is performed, the subscriber stations SS1-1 and SS1-2
may need to wait extra time up to the transmission delay T11.
[0059] FIG. 7 is a fourth sequence diagram of the present invention
being applied to the wireless broadband access system in accordance
with IEEE 802.16.
[0060] The base station BS broadcasts the downlink sub-frame
including UCD, DCD, DL-MAP and UL-MAP (Step S212). The relay
station RS1 broadcasts the downlink sub-frame received from the
base station BS (Step S213). This downlink sub-frame also includes
REG-RSP messages, which are reply against REG-REQ messages sent by
the relay stations RS1 and RS2. The relay stations RS1 and RS2
complete registration process by receiving the REG-RSP message
(Step S214). The relay station RS1 broadcasts a polling packet
during the initial ranging period in the contention slots after
TTG. Preferably, the polling packet may be transmitted based on
CSMA/CA. The polling packet is transmitted after backoff time
period corresponding to the contention windows generated randomly
(Step S215).
[0061] The base station BS and other subscriber stations, as well
as the subscriber stations SS1-1 and SS1-2 receive the polling
packet sent by the relay station RS1. The subscriber stations SS1-1
and SS1-2 shift to contention period state for predetermined period
by receiving the polling packet from the relay station RS1, and are
granted permission to send a RNG-REQ message to the relay station
RS1. However, the base station BS and other stations, which do not
use the relay station RS1, stop sending any packets while the
contention period for the subscriber stations SS1-1 and SS1-2.
[0062] The subscriber station SS1-1 sends a RNG-REQ message to the
relay station RS1 during contention period. The RNG-REQ message is
transmitted after backoff period, such as CSMA/CA method. The
RNG-REQ message includes burst profile, which indicates modulation
type and coding rate to be used between the relay station RS and
the subscriber station SS1-1. (Step S216). The subscriber station
SS1-2 also sends a RNG-REQ message, which has a burst profile, to
the relay station RS1 during contention period (Step S217). The
relay station RS1 sends both RNG-REQ messages from the subscriber
stations SS1-1 and SS1-2 together to the base station BS. The
contents of the RNG-REQ messages from the subscriber stations SS1-1
and SS1-2 are changed before sending it to the base station BS,
because the destination of these messages are changed.
[0063] FIG. 8 shows a frame structure of the polling packet
according the present invention.
[0064] As shown in FIG. 8, the polling packet includes management
message type, which has the value to indicate polling packet,
identification of the relay station RS and time for contention
period for the relayed subscriber stations. Other relay stations
and other subscriber stations do not send any packet during the
time indicated in the polling packet. The subscriber stations that
use the relay station, such as the subscriber stations SS1-1 and
SS1-2, shift to contention period state for the time indicated in
the received polling packet.
[0065] FIG. 9 shows a frame structure of the RNG-REQ message sent
by the subscriber station to the relay station RS. FIG. 10 shows
frame structure of the RNG-REQ message sent by the relay station RS
to the base station BS. The relay station RS changed RNG-REQ shown
in FIG. 9 to RNG-REQ shown in FIG. 10, when the relay station sends
it to the base station BS.
[0066] FIG. 11 is a fifth sequence diagram of the present invention
being applied to the wireless broadband access system in accordance
with IEEE 802.16.
[0067] Step S215 to S217 in FIG. 11 is the same as the step S215 to
S217 in FIG. 7, and is corresponding to step S218 to S220 in FIG.
11, which is the sequence between the relay station RS2 and the
subscriber stations SS2-1 and SS2-2. As shown in FIG. 11, step S215
to S217 and step S218 to S220 can be performed simultaneously. To
do this, initial ranging period in the contention slots can be
reduced. But for simultaneous operation, the different frequency is
assigned for the relay stations RS1 and RS2, or physical distance
between the relay stations RS1 and RS2 must be far enough to avoid
interference, if both relay stations use the same frequency.
[0068] FIG. 12 is a sixth sequence diagram of the present invention
being applied to the wireless broadband access system in accordance
with IEEE 802.16.
[0069] The base station BS broadcasts the downlink sub-frame
including UCD, DCD, DL-MAP and UL-MAP (Step S223). The relay
station RS1 broadcasts the downlink sub-frame including UCD, DCD,
DL-MAP and UL-MAP received from the base station to the relayed
subscriber stations (Step S224). The downlink sub-frame broadcasted
by the base station BS also includes RNG-RSP messages, which are
reply against REG-REQ messages sent by the relay station RS1 (Step
S225), for the subscriber stations SS1-1 and SS1-2. The relay
station RS1 transmits RNG-RSP messages from the base station BS to
the subscriber stations SS1-1 and SS1-2. The subscriber stations
SS1-1 and SS1-2 complete ranging by receiving a RNG-RSP message
from the relay station RS1 (Step S226). The downlink sub-frame
broadcasted by the base station BS also includes RNG-RSP messages,
which are reply against REG-REQ messages sent by the relay station
RS2 (Step S227).
[0070] The relay station RS1 broadcasts a polling packet during the
initial ranging period in the contention slots after TTG. Because
the subscriber stations SS1-1 and SS1-2 have already completed
ranging, the subscriber stations SS1-1 and SS1-2 do not send any
packets. (Step S228).
[0071] The relay station RS1 broadcasts a polling packet during the
bandwidth request period in the contention slots. The polling
packet is transmitted after backoff period, such as CSMA/CA method
(Step S229).
[0072] The base station BS and other subscriber stations, as well
as the relayed subscriber stations SS1-1 and SS1-2 receive the
polling packet sent by the relay station RS1. The subscriber
stations SS1-1 and SS1-2 shift to contention period state for
predetermined time period by receiving the polling packet from the
relay station RS1, and are granted permission to send a BW-REQ
message to the relay station RS1. However, the base station BS and
other stations, which do not use the relay station RS1, stop
sending any packets while the contention slots for the subscriber
stations SS1-1 and SS1-2.
[0073] The subscriber station SS1-1 sends the BW-REQ message for
the registration procedure to the relay station RS1 during the
contention period. The BW-REQ message is transmitted after backoff
period, such as CSMA/CA method. (Step S230). The subscriber station
SS1-2 also sends a BW-REQ message to the relay station RS1 during
contention period (Step S231). The relay station RS1 sends both
BW-REQ messages from the subscriber stations SS1-1 and SS1-2
together to the base station BS. The contents of the BW-REQ from
the subscriber stations SS1-1 and SS1-2 are changed before sending
it to the base station BS, because the destination of these
messages are changed.
[0074] Then, the subscriber stations, which uses relay station RS1,
sends a REG-REQ message based on the UL-MAP to the relay station
RS1, and the relay station RS1 sends the REG-REQ message received
from the subscriber stations to the base station BS. The subscriber
stations SS1-1 and SS1-2 complete registration procedure when they
receive a REG-RSP message from the base station BS via the relay
station RS1. After registration, transmission is performed in
accordance with IEEE 802.16. For the best effort service, the relay
station RS1 relays a BW-REQ message for dynamic service addition
(DSA) using the polling packet.
[0075] The embodiment described here is given merely as example,
and a person skilled in the art can implement other embodiments of
the invention, which are within the scope of the invention.
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